Transistors, and in particular, metal-oxide-semiconductor (“MOS”) field-effect transistors, offer many desirable switch characteristics. Nevertheless, some of their characteristics may render their usage problematic in certain contexts. In particular, the manufacturing process for MOS transistors produces internal junctions between p-type and n-type silicon, yielding parasitic diodes that, when used in such contexts, must be taken into account.
Often, the circuitry employing such transistors is designed to short out such parasitic diodes or to maintain them under reverse bias. Even under reverse bias, however, parasitic diodes exhibit a leakage current. This leakage current can be particularly significant for high voltage (“HV”) MOS transistors, which generally have wider channels and enlarged drain dimensions relative to conventional MOS transistors, resulting in increased PN junction areas and increased injection currents. HV MOS transistors may also suffer from significant sub-threshold current flow. Both the parasitic and sub-threshold currents are temperature-dependent. Such leakage currents may prevent HV MOS transistors from being employed for ultralow current operations, despite their general desirability for their ability to operate at elevated voltages and temperatures.